1. Field of the Invention
The present invention relates to a paper roll braking device for rotary presses adapted to brake the revolution of the paper roll so as to control the running tension of a web that is paid off from the paper roll and caused to travel.
2. Description of the Prior Art
The aforementioned paper roll braking device has already been disclosed in a considerable literature, such as Japanese Published Unexamined Utility Model Application No. Hei-4(1992)-16762, for example. In Japanese Published Unexamined Utility Model Application No. Hei-4(1992)-16762, disclosed are the following three paper roll braking devices:
{circle around (1)} A paper roll braking device comprising an shaft-end braking device having a brake disc fixedly fitted to an end of a paper roll supporting shaft, a pneumatically operated cylinder, and a brake shoe fitted to an end of a cylinder output shaft, in which the tension of a web paid off from a paper roll is detected by a tension sensor connected to a pickup roller disposed on the web traveling path, the detected signal is compared with a predetermined tension value preset in a control section, if the comparison result shows any discrepancy, a control signal is fed from the control section to an electric-pneumatic converter via an amplifier to actuate the electric-pneumatic converter to regulate air pressure to a brake changeover valve, and the regulated air pressure forces the brake shoe onto the brake disc to brake the revolution of the paper roll, thereby controlling the tension of a traveling paper web paid off from the paper roll to a predetermined tension.
{circle around (2)} A paper roll braking device having a surface braking device that forces a plurality of lining belts onto the outer periphery of a paper roll to brake the revolution of the paper roll, thereby controlling the acceleration of the paper roll and the tension of a traveling paper web paid off from the paper roll.
{circle around (3)} A paper roll braking device in which a shaft-end braking device fitted to an end of a paper roll supporting shaft, and a surface braking device that causes a brake belt onto the outer periphery of a paper roll are provided, and the tension of a traveling paper web is controlled by braking the revolution of the paper roll with the surface braking device until after the diameter of the paper roll reaches a predetermined value, and with the shaft-end braking device after the diameter of the paper roll is smaller than the predetermined value.
The foregoing three paper roll braking devices have the following problems and shortcomings.
The paper roll braking device of {circle around (1)} adjusts the tension of the web by forcing the brake shoe onto the brake disc provided on the paper roll supporting member so that the braking force based on the contact friction between the brake disc and the brake shoe is transmitted to the core of the paper roll via the paper roll supporting member to brake the revolution of the paper roll.
With this arrangement, however, the braking force has to be adjusted only by adjusting the contact friction between the brake disc and the brake shoe, regardless of changes in the diameter of the paper roll ranging from a relatively large diameter of a new roll to a smaller diameter immediately before it is used up and spliced to a new one. Consequently, it is extremely difficult to meticulously adjust the tension of the traveling web by braking the revolution of the paper roll whose diameter is reduced gradually in the course of operation.
That is, it is impossible to finely adjust the force of forcing the brake shoe to the brake disc so as to match with the changing rotating inertia of the paper roll whose diameter is gradually reduced in the course of operation. This has led to hunting in the traveling tension of the web; too strong or too weak tension, making the traveling tension unstable and involving much time to stabilize the tension.
In the paper roll braking device of {circle around (2)} whose specific construction is not disclosed, the adjusting accuracy of the traveling tension of the traveling web paid off from the paper roll is not necessarily clear. Broadly speaking, this paper roll braking device forces a lining belt onto the outer periphery of the paper roll to use the contact friction between the lining belt and the paper roll to brake the revolution of the paper roll. The force required for braking differs depending on the type of paper roll, particularly on difference in the surface properties of paper. With paper having an extremely slick or coarse surface, furthermore, it is difficult to satisfactorily adjust the traveling tension of the web. Another shortcoming of this type of paper roll braking device is deterioration of the quality of printed matter due to the damage to the lining belt caused by friction with the surface of the web paid off from the paper roll.
The paper roll braking device of {circle around (3)} brakes the revolution of the paper roll by forcing a braking belt onto the outer periphery of the paper roll, using the contact friction between the braking belt and the paper roll until the diameter of the paper roll is reduced to a predetermined diameter, and by forcing the same brake shoe onto a brake disc fitted to a paper roll supporting shaft to transmit the braking force to the core of the paper roll via the paper roll supporting shaft relying on the contact friction between the brake disc and the brake shoe after the diameter of the paper roll becomes smaller than a predetermined diameter.
Consequently, the paper roll braking device of {circle around (3)} can solve the problem inherent in the paper roll braking device of {circle around (1)}, but cannot resolve the problem inherent in the paper roll braking device of {circle around (2)}. With this device, it is necessary to change over the braking force imparting mechanism for separating the brake belt from the outer periphery and forcing the brake shoe onto the brake disc when the diameter of the paper roll reaches a predetermined value. At this time, however, both the mechanism may be operated simultaneously or disengaged simultaneously, making the traveling tension of the web extremely unstable.
The present invention is intended to overcome these drawbacks by providing a paper roll braking device that makes it possible to meticulously adjust and quickly stabilize the traveling tension of a web paid off from a paper roll by meticulously braking the revolution of the paper roll regardless of the diameter of the paper roll, so that no damage is caused on the surface of the web paid off from the paper roll, and the braking force of the paper roll is prevent from unwantedly increasing or totally disappearing.
It is an object of the present invention to provide a paper roll braking device that makes it possible to meticulously adjust and quickly stabilize the traveling tension of a web paid off from a paper roll by meticulously braking the revolution of the paper roll regardless of the diameter of the paper roll, so that no damage is caused on the surface of the web paid off from the paper roll, and the braking force of the paper roll is prevent from unwantedly increasing or totally disappearing.
It is another object of the present invention to provide an engage/disengage changeover section suitable for causing each friction disc in the braking section to engage with and disengage from both sides of rotors.
It is still another object of the present invention to provide a contact pressure adjusting section that can correct and change the contact pressure of the friction discs to the rotors via the engage/disengage changeover section in accordance with a signal generated by an operation control section.
It is a further object of the present invention to provide a contact pressure adjusting section that controls the traveling tension of a web during normal operation of a rotary press, and can control for emergency stop in a failure of the rotary press.
It is still a further object of the present invention to provide an outside diameter detecting section that detects the outside diameter of a paper roll during operation.
It is still a further object of the present invention to provide an operation control section that generates a correction signal for preventing the slack of the web.
It is still a further object of the present invention to provide an operation control section that generates a splicing signal for splicing a traveling web to a new paper roll to ensure continuous printing.
In disclosed embodiments, a paper roll braking device for rotary presses, in which a web is paid off from a paper roll supported between frames and caused to travel to be printed in printing units, comprising a braking section having rotors provided on paper roll supporting members and frictional discs that are provided at a plurality of locations along the outer periphery of the rotors and can be engaged with and disengaged from the rotors at their respective locations, an engage/disengage changeover section for controlling the engage/disengage operation of the friction discs to the rotors, a contact pressure adjusting section having a tension sensing mechanism for sensing changes in the traveling tension of the web for adjusting the contact pressure of the friction discs to the rotors, an outside diameter detecting section for detecting the outside diameter of the paper roll, an operation controlling section for changing over the engage/disengage changeover section when the paper roll outside diameter detected by the outside diameter detecting section reaches a predetermined diameter.